The present invention relates to a pattern formation method, and more particularly, it relates to a method of forming a resist pattern, used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength of a 1 nm through 180 nm band.
Currently, in fabrication of a large capacity semiconductor integrated circuit, typically such as a 64 Mbit dynamic random access memory (DRAM), a logic device or a system LSI with a 0.25 xcexcm through 0.18 xcexcm rule, a resist pattern is formed by using a resist material including a polyhydroxystyrene derivative as a main component and exposing light of KrF excimer laser (with a wavelength of a 248 nm band).
Moreover, in a pattern formation method under development for a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 xcexcm through 0.13 xcexcm rule, ArF excimer laser operating at a shorter wavelength (of a 193 nm band) than the KrF excimer laser is to be used as the exposing light.
A resist material including a polyhydroxystyrene derivative as a main component includes an aromatic ring having a high absorbing property against light of a wavelength of a 193 nm band. Therefore, the exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film made from this resist material, and hence, a good pattern shape cannot be obtained with this exposing light. Accordingly, the resist material including a polyhydroxystyrene derivative as a main component cannot be used when the ArF excimer laser is used as the exposing light.
Therefore, when the ArF excimer laser is used as the exposing light, a material including, as a main component, a polyacrylic acid derivative free from an aromatic ring is used as a resist material.
On the other hand, X-rays and electron beams (EB) are now examined to be used as exposing light adopted in a pattern formation method applicable to higher resolution.
When X-rays are used as the exposing light, however, there arise various problems in an aligner and formation of amask. Also, when EB is used as the exposing light, there arises a problem of throughput, and hence, EB is not suitable to mass production. Thus, X-rays and EB are not preferred as the exposing light.
Accordingly, in order to form a resist pattern finer than 0.13 xcexcm, it is necessary to use, as the exposing light, a laser beam with a wavelength shorter than that of the ArF excimer laser, such as a Xe2 laser beam (with a wavelength of a 172 nm band), a F2 laser beam (with a wavelength of a 157 nm band), a Kr2 laser beam (with a wavelength of a 146 nm band), an ArKr laser beam (with a wavelength of a 134 nm band), an Ar2 laser beam (with a wavelength of a 126 nm band) or a soft X-ray beam (with a wavelength of a 13, 11 or 5 nm band).
Therefore, the present inventors have formed a resist pattern from a resist film of a known resist material through pattern exposure using a F2 laser beam.
However, the resultant resist pattern does not have a rectangular sectional shape but has a defective pattern shape.
In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using light of a wavelength of a 1 nm through 180 nm band as exposing light.
The present inventors have concluded that the resist pattern has a defective pattern shape because the resist film has a high absorbing property against light of a wavelength of a 1 nm through 180 nm band, and variously studied about resist materials for decreasing the absorbing property against light of a wavelength of a 1 nm through 180 nm band. As a result, it has been found that the peak of a light absorption wavelength determined by a benzene ring is shifted toward a longer wavelength when a hydroxyl group is substituted for a hydrogen atom of the benzene ring, and that as the number of hydroxyl groups substituted for hydrogen atoms of the benzene ring is larger, the peak of the light absorption wavelength is more largely shifted toward a longer wavelength.
FIG. 1 is a diagram of transmittance curves of resist films each with a thickness of 0.1 xcexcm for explaining that as the number of hydroxyl groups substituted for hydrogen atoms of a benzene ring is larger, the peak of a light absorption wavelength is more largely shifted toward a longer wavelength. In FIG. 1, a curve A corresponds to the transmittance curve of a resist film including polystyrene (wherein the number of substituted hydroxyl groups is 0), a curve B corresponds to that of a resist film including poly(p-hydroxystyrene) (wherein the number of substituted hydroxyl groups is 1), a curve C corresponds to that of a resist film including poly(m,p-dihydroxystyrene) (wherein the number of substituted hydroxyl groups is 2), and a curve D corresponds to that of a resist film including poly(m,m,p-trihydroxystyrene) (wherein the number of substituted hydroxyl groups is 3).
As is obvious from FIG. 1, as the number of hydroxyl groups bonded to a benzene ring is larger, the peak of the light absorption wavelength is more largely shifted toward a longer wavelength.
The present invention was devised on the basis of these findings. Specifically, the first pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material containing a base polymer including polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring; and forming a resist pattern by irradiating the resist film with light of a wavelength of a 1 nm through 180 nm band for pattern exposure and developing the resist film with a developer after the pattern exposure.
In the first pattern formation method, since the base polymer of the resist material includes polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring, the peak of a light absorption wavelength determined by the benzene ring is largely shifted toward a longer wavelength. Therefore, the absorbing property against light of a wavelength of a 1 nm through 180 nm band is decreased, and hence, transmittance against the exposing light of a wavelength of a 1 nm through 180 nm band is increased. As a result, a resist pattern can be formed in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as the exposing light.
In the first pattern formation method, solubility of the base polymer in the developer preferably changes in the presence of an acid, and the resist material preferably further contains an acid generator for generating an acid through irradiation with the exposing light.
Thus, a resist pattern with higher sensitivity can be formed in a good pattern shape by using a chemically amplified resist.
In the first pattern formation method, the base polymer is preferably soluble in the developer, and the resist material preferably further contains a crosslinking agent for making the base polymer refractory in the developer by causing crosslinkage of the base polymer through irradiation with the exposing light.
Thus, a negative resist pattern can be formed in a good pattern shape.
In the first pattern formation method, the base polymer is preferably soluble in the developer, and the resist material preferably further contains a dissolution inhibiting agent that inhibits solubility of the base polymer in the developer and decomposes through irradiation with the exposing light.
Thus, a positive resist pattern can be formed in a good pattern shape.
In this case, the dissolution inhibiting agent is preferably a compound in which at least one of hydroxyl groups substituted for hydrogen atoms at two or more portions of a benzene ring of polystyrene is replaced with a protecting group.
Thus, the peak of the light absorption wavelength is further largely shifted toward a longer wavelength, and hence, the transmittance against the exposing light of a wavelength of a 1 nm through 180 nm band is further increased.
The second pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material containing a base polymer including polystyrene in which at least one of hydroxyl groups substituted for hydrogen atoms at two or more portions of a benzene ring is replaced with a protecting group; and forming a resist pattern by irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band for pattern exposure and developing the resist with a developer after the pattern exposure.
In the second pattern formation method, since the resist material contains the base polymer including polystyrene in which at least one of hydroxyl groups substituted for hydrogen atoms at two or more portions of a benzene ring is replaced with a protecting group, the peak of the light absorption wavelength determined by the benzene ring is largely shifted toward a longer wavelength. Therefore, the absorbing property against light of a wavelength of a 1 nm through 180 nm band is increased, and hence, the transmittance against the exposing light of a wavelength of a 1 nm through 180 nm band is increased. As a result, a resist pattern can be formed in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as the exposing light.
In the second pattern formation method, solubility of the base polymer in the developer preferably changes in the presence of an acid, and the resist film preferably further contains an acid generator for generating an acid through irradiation with the exposing light.
Thus, a resist pattern with higher sensitivity can be formed in a good pattern shape by using a chemically amplified resist.
The third pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material containing a copolymer of a compound including polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring and a compound in which at least one of hydroxyl groups substituted for hydrogen atoms at two or more portions of a benzene ring is replaced with a protecting group; and forming a resist pattern by irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band for pattern exposure and developing the resist film with a developer after the pattern exposure.
In the third pattern formation method, since the base polymer of the resist material contains the copolymer of the compound including polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring and the compound in which at least one of hydroxyl groups substituted for hydrogen atoms at two or more portions of a benzene ring is replaced with a protecting group, the peak of the light absorption wavelength determined by the benzene rings is largely shifted toward a longer wavelength. Therefore, the absorbing property against light of a wavelength of a 1 nm through 180 nm band is decreased, and hence, the transmittance against the exposing light of a wavelength of a 1 nm through 180 nm band is increased. As a result, a resist pattern can be formed in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as the exposing light.
In the third pattern formation method, solubility of the base polymer in the developer preferably changes in the presence of an acid, and the resist material preferably further contains an acid generator for generating an acid through irradiation with the exposing light.
Thus, a resist pattern with higher sensitivity can be formed in a good pattern shape by using a chemically amplified resist.
The fourth pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material containing a base polymer including polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring; irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band for pattern exposure and forming an organic metal film in a surface region of an unexposed portion of the resist film after the pattern exposure; and forming a resist pattern from the unexposed portion of the resist film by etching the resist film with the organic metal film used as a mask.
In the fourth pattern formation method, since the base polymer of the resist material includes polystyrene in which hydroxyl groups are substituted for hydrogen atoms at two or more portions of a benzene ring, the peak of the light absorption wavelength determined by the benzene ring is largely shifted toward a longer wavelength. Therefore, the absorbing property against light of a wavelength of a 1 nm through 180 nm band is decreased, and hence, the transmittance against the exposing light of a wavelength of a 1 nm through 180 nm band is increased. As a result, a resist pattern can be formed in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as the exposing light.
Furthermore, in the fourth pattern formation method, since the concentration of the hydroxyl groups in the resist film is high, the organic metal film formed in the surface region of the unexposed portion of the resist film attains high density. This increases the etch selectivity between the exposed portion and the unexposed portion of the resist film. As a result, the resultant resist pattern can attain high resolution.
In any of the first through fourth pattern formation methods, the exposing light is preferably a F2 laser beam or an Ar2 laser beam.